Image forming apparatus

ABSTRACT

An image forming apparatus having a communication interface receives image data through the communication interface to form an image. The image forming apparatus includes a power supply unit, a states monitor unit, and a mode switch unit. The power supply unit supplies electric power either in an operation mode in which the electric power necessary to form the image is supplied or in a power saving mode in which stand-by electric power is supplied. The states monitor unit monitors a connection state and a non-connection state of the communication interface. In the power saving mode, the mode switch unit switches the power supply unit to the operation mode, in response to detection by the states monitor unit of either of a change from the non-connection state to the connection state or a change from the connection state to the non-connection state.

BACKGROUND

1. Technical Field

The present invention relates to an image forming apparatus having apower saving function.

2. Related Art

Recently the image forming apparatus having a power saving function iswidely used in printers and copying machines. For example, it is knownthat a controller including a determination unit and an automaticsetting unit. For a parallel interface control circuit, a serialinterface control circuit, a network interface control circuit, and thelike which are of the communication interface control circuit, thedetermination unit determines whether a computer is connected to each ofcommunication interface control circuits or not. When the determinationunit determines that the computer is not connected to the communicationinterface control circuit, the automatic setting unit individually setsthe communication interface control circuit in a power saving mode. Inthe controller, negotiation is required for the connection between thecommunication interface and the computer, and it is determined whetherthe connection with the computer is completed or not according to thenegotiation status. When a signal is inputted to the interface switchedto the power saving mode, the power saving mode is automaticallyreleased.

In a peripheral device (for example, printer), such as USB (UniversalSerial Bus) and IEEE (American Institute of Electrical Engineers) 1394,which has the communication interface including a power line forindicating a potential a predetermined value or more when thecommunication is enabled, for example, it is known that a peripheraldevice which monitors the potentials of the power lines of thecommunication interfaces and the energy saving of the peripheral deviceis performed when the potential of the power line is decreased apredetermined value or less.

SUMMARY

An aspect of the image forming apparatus of the present invention has acommunication interface which mediates data communication, the imageforming apparatus receiving image data through the communicationinterface to form an image based on the received image data, the imageforming apparatus including: a power supply unit which supplies electricpower in any one of power supply modes of an operation mode in which theelectric power necessary to form the image is supplied, and a powersaving mode in which stand-by electric power is supplied; a statesmonitor unit which monitors a connection state and a non-connectionstate of the communication interface; and a mode switch unit whichswitches the power supply unit to the operation mode, in response todetection by the states monitor unit of either of a change from thenon-connection state to the connection state or a change from theconnection state to the non-connection state, when the power supply unitis in the power saving mode.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiment(s) of the present invention will be described in detail basedon the following figures, wherein:

FIG. 1 is a schematic view showing an electrophotographic full-colorprinter which is of an example of an image forming apparatus accordingto the embodiment of the present invention;

FIG. 2 is a block diagram showing the image forming apparatus having apower saving function according to the embodiment of the presentinvention;

FIG. 3 is a block diagram showing a power saving function in aconventional image forming apparatus;

FIG. 4(a) and FIG. 4(b) show a method of detecting a connection stateand a non-connection state of a USB interface according to theembodiment;

FIG. 5(a) and FIG. 5(b) show a method of detecting the connection stateand the non-connection state of an Ethernet interface according to theembodiment;

FIG. 6 is a timing chart showing mode switch of the USB interfaceaccording to the embodiment;

FIG. 7 is a flowchart showing a process of switching image formingapparatus from an operation mode to a power saving mode according to theembodiment; and

FIG. 8 is a flowchart showing an interruption process according to theembodiment.

DETAILED DESCRIPTION

Embodiment(s) of the present invention will be described below withreference to the drawings.

FIG. 1 is a schematic view showing an electrophotographic full-colorprinter which is of an example of an image forming apparatus accordingto the embodiment of the present invention.

Referring to FIG. 1, the full-color printer has an image forming unitincluding a photosensitive drum (hereinafter simply referred to as“photosensitive body”) 1, a charging roller 8, an exposure device 9, adevelopment assembly 10, an intermediate transfer belt 3, a primarytransfer device 2, a cleaner device 27, a secondary transfer device 4, abelt cleaner 16, recording-paper cassettes 17 and 18,drawing rollers 19and 20, roller pairs 21, 22, and 23, a fixing device 24, and paper-exittrays 25 and 26. The photosensitive body 1 is rotated in a direction ofan arrow A. The charging roller 8 charges the photosensitive body 1. Theexposure device 9 irradiates the photosensitive body 1 with exposurelight to form an electrostatic latent image. The development assembly 10develops the electrostatic latent image formed on the photosensitivebody 1 using toner. The intermediate transfer belt 3 receives transferof the toner image formed on photo sensitive body 1. The primarytransfer device 2 transfers the toner image, formed on thephotosensitive body 1, to the intermediate transfer belt 3. The cleanerdevice 27 removes the toner which remains on the photosensitive body 1after the toner image is transferred to the intermediate transfer belt3. The secondary transfer device 4 transfers the toner image,transferred to the intermediate transfer belt 3, to the recording paper.The belt cleaner 16 removes the toner which remains on the intermediatetransfer belt 3 after the toner image is transferred to the recordingpaper. The pieces of recording paper are accommodated in therecording-paper cassettes 17 and 18. The drawing rollers 19 and 20 drawthe recording paper from the recording-paper cassettes 17 and 18respectively. The roller pairs 21, 22, and 23 feed the recording paper,drawn into a conveyance path by drawing roller 19 or 20, to a nipportion between the intermediate transfer belt 3 and the secondarytransfer device 4. The fixing device 24 fixes the toner image,transferred from the intermediate transfer belt 3, onto the recordingpaper. The recording paper to which the fixation has been performedexits to the paper-exit tray 25 or 26.

In addition to the image forming unit, the full-color printer includes acontrol unit 52, a power supply unit 53, a states monitor unit 57, amode switch unit 58, and a communication function switch unit 59, andthese units perform the power saving function of the image formingapparatus of the embodiment. The units will be described in detaillater.

The development assembly 10 includes four development devices 10Y, 10M,10C, and 10K for full-color development. The development devices 10Y,10M, 10C, and 10K develop the electrostatic latent images on thephotosensitive body 1 with yellow (Y) toner, magenta (M) toner, cyan (C)toner, and black (B) toner respectively. In developing the electrostaticlatent image with each color of toner, the development assembly 10 isrotated in a direction of an arrow R by a motor (not shown), and theelectrostatic latent image is aligned such that the development devicehaving the corresponding color abut on the photosensitive body 1.

The four-color toner images developed on the photosensitive body 1 aresequentially transferred to the intermediate transfer belt 3 by theprimary transfer device 2, and four-color toner images are superposed onthe photosensitive body 1. The intermediate transfer belt 3 is tensionedby rollers 12, 13, 14, and 15. The roller 12 functions as a drive rollerconnected to a drive source (not shown) to drive the intermediatetransfer belt 3. The roller 13 functions as a tension roller whichadjusts tension of the intermediate transfer belt 3. The roller 14functions as a backup roller of the secondary transfer device 4.

The belt cleaner 16 is provided at a position where the belt cleaner 16faces the roller 15 across the intermediate transfer belt 3, and theremaining toner on the intermediate transfer belt 3 is scraped out witha cleaner blade.

The recording paper drawn into the conveyance path from therecording-paper cassette 17 or 18 by the drawing roller 19 or 20 is fedto the nip portion, i.e., to the abutment portion of the secondarytransfer device 4 and the intermediate transfer belt 3 by the rollerpairs 21, 22, and 23.

The toner image formed on the intermediate transfer belt 3 istransferred onto the recording paper at the nip portion, the toner imageis fused and fixed to the recording paper by the fixing device 24, andthe recording paper exits to the paper-exit tray 25 or 26.

A reflection type optical sensor 6 is arranged while facing theintermediate transfer belt 3, and the optical sensor 6 detects lightreflected from a reflection foil 5 on the intermediate transfer belt 3.A detection signal of the reflected light is utilized as a referencesignal for controlling timing for image forming by the exposure device 9or toner-image transfer.

Each of the development devices 10Y, 10M, 10C, and 10K includes anexchangeable toner cartridge (not shown), a development roller (notshown) which imparts a development bias, a toner supply device (notshown) which supplies the toner to the development roller, and aconveyance device (not shown).

A process of forming the image with the full-color printer having theabove configuration will be described below.

A voltage is applied to the charging roller 8 to uniformly charge asurface of the photosensitive body 1 at a predetermined negativepotential of the charged portion. The exposure device 9 performs theexposure such that an image portion on the charged photosensitive body 1becomes a predetermined potential of the exposed portion, which allowsthe electrostatic latent image to be formed. That is, the electrostaticlatent image corresponding to the image is formed by turning on and offthe exposure device 9 based on an image signal supplied from a controldevice (not shown).

The development bias is applied to the development rollers of thedevelopment devices 10Y, 10M, 10C, and 10K, and the development bias ispreviously set in each color. When the electrostatic latent imagepassing through the position of the development roller, theelectrostatic latent image is developed with the toner and visualized asthe toner image. The toner image is transferred to the intermediatetransfer belt 3 by the primary transfer device 2, and the toner image istransferred to the recording paper by the secondary transfer device 4.Then, the toner image is conveyed to the fixing device 24. In thefull-color printing, after the four colors of the toner are superposedon the belt, the four colors of the toner are transferred to therecording paper. The toner remaining on the photosensitive body 1 isremoved and collected by the cleaner device 27.

The power saving function of the image forming apparatus of theembodiment will be described below.

FIG. 2 is a block diagram showing an image forming apparatus having apower saving function according to the embodiment of the presentinvention.

Referring to FIG. 2, an image forming apparatus 50 includes an imageforming unit 51, the power supply unit 53, a USB interface 54, anEthernet interface 55, a video interface 56, the states monitor unit(interruption controller) 57, the mode switch unit (CPU: CentralProcessing Unit) 58, and a switch S1 (59 a), a switch S2 (59 b), and aswitch S3 (59 c). The image forming unit 51 has the same configurationas the full-color printer shown in FIG. 1. The image forming unit 51includes a communication interface which mediates data communication.The image forming unit 51 receives image data through the communicationinterface to form the image based on the received image data. The powersupply unit 53 supplies the electric power in one of power supply modesof an operation mode and a power saving mode. The electric powernecessary to the image formation is supplied in the operation mode, andstand-by electric power is supplied in the power saving mode. The USBinterface 54 receives the image data inputted through a USB cable. TheEthernet interface 55 receives the image data inputted through Ethernet.The video interface 56 outputs the image data to the image forming unit51. The states monitor unit 57 monitors a connection state and anon-connection state of each of the communication interfaces. In thecase where either of a change from the non-connection state to theconnection state or a change from the connection state to thenon-connection state is detected by the states monitor unit 57 while thepower supply unit 53 is in the power saving mode, the mode switch unit58, in response to the detection, switches the power supply unit 53 tothe operation mode. The switch S1 (59 a), the switch S2 (59 b), and theswitch S3 (59 c) turn on and off the USB interface 54, the Ethernetinterface 55, and the video interface 56 respectively. The switches S1,S2, and S3 are turned on and off by the control from the power supplyunit 53.

The switch S1 (59 a), the switch S2 (59 b), and the switch S3 (59 c) inthe embodiment correspond to the communication function switch unit 59.Further, in the embodiment, the power supply unit 53 has thecommunication function switch unit 59 which switches the communicationinterface in the power saving mode between a communication enabling modeand a communication disabling mode. When the operation mode is switchedto the power saving mode, the mode switch unit 58 is configured tomaintain the communication interface at the communication enabling modeor to transfer the communication interface to the communicationdisabling mode, according to the connection mode or non-connection modeof the communication interface which is detected by the states monitorunit 57. Operation electric power necessary to data communicationperformed by the communication interface is supplied in communicationenabling mode, and stand-by electric power having a communicationdisabled level is also supplied to the communication interface in thecommunication disabling mode.

A block diagram of the power saving function in a conventional imageforming apparatus will be shown by way of reference example.

FIG. 3 is a block diagram showing the power saving function in theconventional image forming apparatus.

Referring to FIG. 3, the image forming apparatus includes a USBinterface 91, an Ethernet interface 92, and a video interface 95 whichare of the communication interface mediating the data communication. Theimage forming apparatus also includes CPU 94, an interruption controller93, and an image forming unit 96. In the conventional image formingapparatus, for USB, when the USB cable is connected to a USB connector91 a, a USB interface 91 c asserts IRQ (Interrupt Request) 0 of theinterruption controller 93 to post the connection of the USB connector91 a to CPU 94, CPU 94 turns on USB pull-up to cause DMA (Direct MemoryAccess) to be in a start state, and CPU 94 performs the control suchthat the data can be transmitted and received through the USB interface91.

In the power saving mode, it is desirable that the operation of theunnecessary functional block be stopped as much as possible. Therefore,when the USB cable is in the non-connection state in switching the imageforming apparatus to the power saving mode, it is necessary to stop thefunction of the USB interface 91 c. In the conventional technology shownin FIG. 3, whether VBUS 91 b which is of a power line of the USBinterface 91 c exceeds a predetermined potential or not is determined byreading the potential level of an input port PU of the USB interface 91c through a software program, and thereby it is determined whether theUSB is in the connection state or in the non-connection state. However,when the USB cable is connected to the USB connector 91 a at the sametime when the image forming apparatus is switched to the power savingmode, sometimes the potential of VBUS 91 b becomes unstable due tochattering. In this case, an L level (USB is in the non-connectionstate) is read as a value of the input port. As a result, although theUSB cable is connected, the USB functional block is stopped, whichcauses a problem that the image forming apparatus enters the powersaving mode while the communication cannot be performed.

Therefore, as shown in FIG. 2, the image forming apparatus of theembodiment includes the power supply unit 53, the states monitor unit57, and the mode switch unit 58. The power supply unit 53 supplies theelectric power in one of the power supply modes of the operation mode,in which the electric power necessary to the image formation issupplied, and the power saving mode in which the stand-by electric poweris supplied. The states monitor unit 57 monitors the connection stateand the non-connection state of each of the communication interfaces(USB interface 54 and Ethernet interface 55). In the case where eitherof a change from the non-connection state to the connection state or achange from the connection state to the non-connection state is detectedby the states monitor unit 57 while the power supply unit 53 is in thepower saving mode, the mode switch unit 58, in response to thedetection, switches the power supply unit 53 to the operation mode.

According to the image forming apparatus of the embodiment, for example,when the states monitor unit 57 detects transition of the potential of asignal line 54 b indicating the connection state of the USB interface54, the mode switch unit 58 causes the power supply unit 53 to transferto the operation mode according to the detection and causes theinterface to be in the communication enabling state, when either of achange from the non-connection state to the connection state or a changefrom the connection state to the non-connection state is detected.Therefore, because the power supply unit 53 is prevented from transitingto the power saving mode while the chattering does not sink down,usability can be improved such that the generation of incompletedata-capture is prevented.

For the Ethernet interface 55, a PHY chip 55 b located in a post-stageof an Ethernet connector 55 a is connected to IRQ3 of the interruptioncontroller 57, and presence or absence of data link establishment, i.e.,either of a change from the non-connection state to the connection stateor a change from the connection state to the non-connection state isdetected by a LINK status output signal 55 c of the PHY chip 55 b. Inresponse to the detection of either of a change, the mode switch unit 58switches the power supply unit 53 to the operation mode.

With reference to the preferable method of detecting the change inconnection state in the USB interface 54 and the Ethernet interface 55,there is a method of inputting a potential signal and the LINK statusoutput signal 55 c of VBUS 54 b to the interruption controller 57 todetect edges of the signals with the interruption controller 57.

FIG. 4(a) and FIG. 4(b) show a method of detecting the connection stateand the non-connection state of the USB interface.

As shown in FIG. 4(a), when the USB interface 54 (see FIG. 2) is in theconnection state, VBUS 54 b is in an H level and can only transit to theL level. Therefore, as shown in FIG. 4(b), fall-edge detection is set inthe interruption setting. Alternatively, when the USB interface 54 is inthe non-connection state, VBUS 54 b is in the L level and can onlytransit to the H level. Therefore, rise-edge detection is set in theinterruption setting. The mode switch unit (CPU) 58 switches the powersaving mode to the operation mode based on the interruptions.

Examples of the method of determining whether the USB interface is inthe connection state include a method of reading a VBUS input signallevel of the USB interface through a software program and a method inwhich the connection state of the USB interface is evaluated byavailability of communication through the USB interface. However, thepresent invention is not particularly limited to the above methods.

FIG. 5(a) and FIG. 5(b) show a method of detecting the connection stateand the non-connection state of the Ethernet interface.

In the case of the Ethernet interface, the connection and thenon-connection of the interface is evaluated by utilizing acharacteristic in which the data is not transmitted and received unlessthe data link is established. As shown in FIG. 5(a), when the data linkis established, the LINK status output signal 55C of the PHY chip 55 bis in the assert state (H level in the embodiment) and can only transitto the L level. Therefore, as shown in FIG. 5(b), the fall-edgedetection is set in the interruption setting. When the data link is notestablished, the LINK status output signal 55C is in a negate state (Llevel) and can only transit to the H level. Therefore, the rise-edgedetection is set in the interruption setting. The mode switch unit (CPU)58 switches the power saving mode to the operation mode based on theinterruptions.

Examples of the method of determining whether the Ethernet interface isin the connection state include a method of reading the LINK statusoutput signal 55C of the Ethernet interface through a software programand a method in which the connection state of the Ethernet interface isevaluated by availability of communication through the Ethernetinterface. However, the present invention is not particularly limited tothe above methods.

FIG. 6 is a timing chart showing the mode switch of the USB interface inthe embodiment.

As shown in FIG. 6, for the image forming apparatus in the operationmode, when the data is not inputted and outputted for a predeterminedtime, a timer 61 (see FIG. 2) times out to switch the image formingapparatus to the power saving mode (time t1). When the USB cable isconnected to the USB connector 54 a (see FIG. 2) during the power savingmode (time t2), CPU is interrupted (INT) because the potential of VBUSis changed (time t3), which releases the power saving mode to start thetransition to the operation mode (time t4). After the image formingapparatus is switched from the power saving mode to the operation modeto prepare the reception of the data from the USB interface, thecommunication with a host device is started (time t5) by turning on theUSB pull-up 54 c and ended (time t6) to shift to the operation mode.

The above operation performed in the embodiment can avoid a risk offalling into malfunction such as the generation of the incompletedata-capture, unlike the technique disclosed in Japanese PatentLaid-Open No. 2000-353032 in which the connection state is falselydetected due to the chattering when the USB connector is inserted inswitching the image forming apparatus from the power saving mode to theoperation mode.

The USB interface has a scheme in which the availability of the datatransfer is posted to the host device side by pulling up a positiveelectrode side D+ of differential data lines D+ and D− (see FIG. 2).When the pull-up is off, the data communication is not performed even ifthe host device is electrically connected to the device to becommunicated. When the USB interface is in the non-connection state, theimage forming apparatus is switched to the power saving mode while thepull-up is off.

A modification of the embodiment may be configured to inform the hostdevice by the NAK reply that data cannot be received as a protocol ofthe USB interface. For the case of a commercially available USBinterface IC, IC has a function of automatically performing the NAKreply when the data cannot be received because a reception buffer isfilled up in IC. An embodiment in which the function of automaticallyperforming the NAK reply is used will be described below. In theembodiment, even if the USB interface is in the non-connection state,DMA is caused to be in the stopped stated while the pull-up is on, andthe image forming apparatus is switched to the power saving mode. Whenthe USB interface is connected in the power saving mode, because thepotential of the power line VBUS 54 b (see FIG. 2) is changed, the imageforming apparatus is returned to the operation mode from the powersaving mode according to the change in potential of the power line VBUS54 b. At the same time, the reception data is stored in the receptionbuffer in IC since DMA is not started in the USB interface IC, and thenthe host device temporarily stop the data transfer because ICautomatically sends the NAK reply when the reception buffer is filledup. When the return to the operation mode from the power saving mode isfinished, DMA is started in the USB interface IC, which starts a processof transferring the reception data to RAM to resume the USB datareceiving operation.

For the image forming apparatus of the embodiment having the pluralcommunication interfaces, in the mode switch process associated with thechange in connection state of the communication interface, the processis performed only in the portion where the data may be transmitted andreceived by the communication interface whose connection state ischanged.

For example, when only the USB interface is changed from thenon-connection state to the connection state, the portion associatedwith the data transmission and reception of Ethernet, i.e., MAC (MediaAccess Controller) 55 d is kept in the power saving mode, which allowsthe power saving effect to be further improved.

The process of switching the image forming apparatus of the embodimentfrom the operation mode to the power saving mode will be describedbelow.

FIG. 7 is a flowchart showing the process of switching the image formingapparatus from the operation mode to the power saving mode, and FIG. 8is a flowchart showing the interruption process.

As shown in FIG. 7, after the power is turned on, a status value of“prohibition” is written in an energy saving switch flag which is of asoftware variable (Step S01). In Step S02, it is determined whether theenergy saving switch flag is set at “prohibition” or not. The energysaving switch flag is set at either “permission” or “prohibition”through the interruption process shown in FIG. 8. The flow stays in StepS02 until the energy saving switch flag is updated through theinterruption process.

In the interruption process shown in FIG. 8, when any one of IRQ0 toIRQ4 of the interruption controller (states monitor unit) 57 (see FIG.2) is asserted, CPU (mode switch unit) 58 is interrupted. In the casewhere CPU 58 is in the power saving mode which is CPU 58's own energysaving function, CPU 58 is automatically switched from the power savingmode to the operation mode, and the INT process is started (Step S11).

As shown in FIG. 2, IRQ0 of the interruption controller 57 monitors theevent of the data transmission and reception from the USB interface 54,IRQ1 monitors the potential of the power line VBUS 54 b of the USBinterface 54, IRQ2 monitors the event of the data transmission andreception from MAC 55 d of the Ethernet interface 54, and IRQ3 monitorsthe LINK status of the PHY chip 55 b of the Ethernet interface 54, andIRQ4 monitors the time-out of the timer 61.

When the interruption process (see FIG. 8) is started in Step S11, inStep S12 it is determined whether IRQ4 is asserted or not.

In Step S12, when it is determined that IRQ4 is asserted, namely, whenthe timer 61 times out, the energy saving switch flag is updated to“permission” (Step S13), the timer 61 is stopped (Step S14), and theflow goes to Step S15.

On the other hand, when it is determined that IRQ4 is not asserted, theflow goes to Step S15.

In Step S15, it is determined whether IRQ1 or IRQ3 is asserted or not.

In Step S15, when it is determined that IRQ1 or IRQ3 is asserted, theflow goes to Step S16. In Step S16, the electric power is supplied tothe interfaces by closing the switch S1 (59 a) arranged between thepower supply unit 53 and the USB interface 54, the switch S2 (59 b)arranged between the power supply unit 53 and MAC 55 d of the Ethernetinterface 55, and the switch S3 (59 c) arranged between the power supplyunit 53 and the video interface 56. After the timer 61 is reset, thecount operation is started (Step S17). Then, the energy saving switchflag is updated to “prohibition” (Step S18), and the flow goes to StepS19.

On the other hand, when it is determined that both IRQ1 and IRQ3 are notasserted, the flow goes to Step S19.

In Step S19, it is determined whether IRQ0 or IRQ2 is asserted or not.

In Step S19, when it is determined that IRQ0 or IRQ2 is asserted,namely, when it is determined that the USB data or the Ethernet data isreceived, the flow goes to Step S20 In Step S20, the DMA controller 62is caused to be started.

In Step S21, it is determined whether the data has the necessity toreturn to the operation mode from the power saving mode or not.

In Step S21, when it is determined that the data has the necessity toreturn to the operation mode from the power saving mode, the flow goesto Step S22. In Step S22, the electric power is supplied to theinterfaces by closing the switch S1 (59 a) arranged between the powersupply unit 53 and the USB interface 54, the switch S2 (59 b) arrangedbetween the power supply unit 53 and MAC 55 d of the Ethernet interface55, and the switch S3 (59 c) arranged between the power supply unit 53and the video interface 56. After the timer 61 is reset, the countoperation is started (Step S23). Then, the energy saving switch flag isupdated to “prohibition” (Step S24), and the flow goes to Step S25.

On the other hand, when it is determined that the data does not have thenecessity to return to the operation mode from the power saving mode,the flow goes to Step S25.

Also, in Step S19, when it is determined that both IRQ0 and IRQ2 areasserted, the flow goes to Step S25.

In Step S25, the interruption factor is cleared, and the interruptionprocess shown in FIG. 8 is ended.

When the interruption process is ended, the flow returns to Step S02 ofthe flowchart shown in FIG. 7.

In Step S02 of the flowchart shown in FIG. 7, it is determined whetherthe energy saving switch flag is in the status of “prohibition” or“permission”.

In Step S02, because the energy saving switch flag is in the“prohibition” status until the timer 61 (see FIG. 2) times out, thestandby state is maintained.

On the other hand, in Step S02, when the energy saving switch flag ischanged to the “permission” status, the flow goes to Step S03. In StepS03, it is determined whether the signal level in VBUS 54 b of the USBinterface 54 (see FIG. 2) is in the L level or the H level.

In Step S03, when it is determined that the signal level in VBUS 54 b isin the L level, it is determined that USB is in the non-connectionstate, and the switch S1 (59 a) is turned off to stop the electric powersupply to the USB interface (Step S04). Then, the flow goes to Step S05.

On the other hand, in Step S03, when it is determined that the signallevel in VBUS 54 b is in the H level, the flow goes directly to StepS05.

In Step S05, a LINK status is detected in the PHY chip 55 b of theEthernet interface, and it is determined whether the LINK status is LINKDown or LINK Up.

In Step S05, when it is determined that the LINK status is LINK Down, itis determined that Ethernet is in the non-connection state, and theswitch S2 (59 b) is turned off to stop the electric power supply to MAC55 d of the Ethernet interface (Step S06). Then, the flow goes to StepS07.

On the other hand, when it is determined that the LINK status is LINKUp, the flow goes directly to Step S07.

In Step S07, the switch S3 (59 c) is turned off to stop the electricpower supply to the video interface 56, and then the process of CPU 58is stopped by switching the CPU 58 to the power saving mode.

As described above, when any one of the interruptions of IRQ0 to IRQ3 isgenerated, CPU 58 returns to the operation mode from the power savingmode. Because the timer 61 is stopped in the power saving mode, theinterruption is not generated in IRQ4.

With reference to the function of automatically returning to theoperation mode from the power saving mode when the interruption to CPU58 is asserted, the embodiment utilizes the function incorporated in thegeneral-purpose CPU, so that the detailed description will be omitted.

On the other hand, when the data does not have the necessity to returnto the operation mode from the power saving mode although IRQ0 or IRQ2is asserted by receiving the data from the USB interface or the Ethernetinterface, for example, when the data is a ping command or an ARP(Address Resolution Protocol) command, the interruption process is endedwhile the energy saving switch flag is not changed, i.e., while theenergy saving switch flag is kept in “permission”. When the interruptionprocess is ended, the energy saving switch flag is kept in “permission”,the determination of the connection state is made for the USB interfaceor the Ethernet interface, and the video interface is turned off. Then,CPU performs the switch operation to the power saving mode again.

Thus, according to the image forming apparatus of the embodiment havingthe above configuration, the malfunction never occurs even if thecommunication interface is connected during switching the image formingapparatus from the operation mode to the power saving mode and duringthe power saving mode, and the power consumption in the power savingmode can be decreased more than a conventional technique.

According to the image forming apparatus of the embodiment having theabove configuration, when the signal is inputted to the interfaceswitched to the power saving mode from the operation mode before theinterface returns to the operation mode again, the incomplete inputdata-capture can be prevented.

The power supplyunit may include a communication function switch unitwhich switches, in the power saving mode, the communication interfacebetween a communication enabling mode in which operating electric powernecessary for data communication performed by the communicationinterface is supplied to the communication interface, and acommunication disabling mode in which stand-by electric power having alevel at which communication is disabled is supplied to thecommunication interface. The power supply unit also may include the modeswitch unit causes the communication interface to be kept in thecommunication enabling mode according to the connection state of thecommunication interface detected by the states monitor unit, and themode switch unit causes the communication interface to be switched tothe communication disabling mode according to the non-connection stateof the communication interface detected by the states monitor unit, whenthe operation mode is switched to the power saving mode.

According to the image forming apparatus of the embodiment having theabove configuration, the image forming apparatus can be operated moresecurely.

Additionally, the image forming apparatus of the embodiment may includea communication interface having a power line, wherein the statesmonitor unit detects the connection state and the non-connection stateof the communication interface based on a potential of the power line ofthe communication interface.

According to the image forming apparatus of the embodiment having theabove configuration, for example, when the USB interface is used as thecommunication interface, the connection state and the non-connectionstate of the communication interface can be detected based on thepotential of the power line of USB. Therefore, the image formingapparatus of the embodiment can easily be realized.

Moreover, the image forming apparatus of the embodiment may include acommunication interface which mediates the data communication while adata link is established, wherein the states monitor unit detects theconnection state and the non-connection state of the communicationinterface based on presence or absence of the data link establishment ofthe communication interface.

According to the image forming apparatus of the embodiment having theabove configuration, for example when the Ethernet interface is used asthe communication interface, the connection state and the non-connectionstate of the communication interface can be detected based on a LINKstatus output signal of a PHY chip of the Ethernet interface. Therefore,the image forming apparatus of the embodiment can easily be realized.

Thus, the image forming apparatus in which malfunction can be preventedin switching the modes and power consumption in the power saving modecan be decreased more than ever can be realized according to theembodiment.

The foregoing description of the embodiments of the present inventionhas been provided for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Obviously, many modifications and variationswill be apparent to practitioners skilled in the art. The embodimentswere chosen and described in order to best explain the principles of theinvention and its practical applications, thereby enabling othersskilled in the art to understand the invention for various embodimentsand with the various modifications as are suited to the particular usecontemplated. It is intended that the scope of the invention be definedby the following claims and their equivalents.

Lastly, the entire disclosure of Japanese Patent Application PublicationNo. 2005-339552 including specification, claims, drawings and abstractis incorporated herein by reference in its entirety.

1. An image forming apparatus having a communication interface whichmediates data communication, the image forming apparatus receiving imagedata through the communication interface to form an image based on thereceived image data, the image forming apparatus comprising: a powersupply unit which supplies electric power in any one of power supplymodes of an operation mode in which the electric power necessary to formthe image is supplied, and a power saving mode in which stand-byelectric power is supplied; a states monitor unit which monitors aconnection state and a non-connection state of the communicationinterface; and a mode switch unit which switches the power supply unitto the operation mode, in response to detection by the states monitorunit of either of a change from the non-connection state to theconnection state or a change from the connection state to thenon-connection state, when the power supply unit is in the power savingmode.
 2. An image forming apparatus according to claim 1, wherein thepower supply unit includes a communication function switch unit whichswitches, in the power saving mode, the communication interface betweena communication enabling mode and a communication disabling mode, thecommunication enabling mode in which operating electric power necessaryfor data communication performed by the communication interface issupplied to the communication interface, the communication disablingmode in which stand-by electric power having a level at whichcommunication is disabled is supplied to the communication interface,and the mode switch unit causes the communication interface to be keptin the communication enabling mode according to the connection state ofthe communication interface detected by the states monitor unit, and themode switch unit causes the communication interface to be switched tothe communication disabling mode according to the non-connection stateof the communication interface detected by the states monitor unit, whenthe operation mode is switched to the power saving mode.
 3. An imageforming apparatus according to claim 1, comprising a communicationinterface having a power line, wherein the states monitor unit detectsthe connection state and the non-connection state of the communicationinterface based on a potential of the power line of the communicationinterface.
 4. An image forming apparatus according to claim 2,comprising a communication interface having a power line, wherein thestates monitor unit detects the connection state and the non-connectionstate of the communication interface based on a potential of the powerline of the communication interface.
 5. An image forming apparatusaccording to claim 1, comprising a communication interface whichmediates the data communication while a data link is established,wherein the states monitor unit detects the connection state and thenon-connection state of the communication interface based on presence orabsence of the data link establishment of the communication interface.6. An image forming apparatus according to claim 2, comprising acommunication interface which mediates the data communication while adata link is established, wherein the states monitor unit detects theconnection state and the non-connection state of the communicationinterface based on presence or absence of the data link establishment ofthe communication interface.
 7. An image forming apparatus having acommunication interface which mediates data communication, the imageforming apparatus receiving image data through the communicationinterface to form an image based on the received image data, the imageforming apparatus comprising: a power supply unit which supplieselectric power in any one of power supply modes of an operation mode inwhich the electric power necessary to form the image is supplied, and apower saving mode in which stand-by electric power is supplied; a statesmonitor unit which monitors a connection state and a non-connectionstate of the communication interface; and a mode switch unit whichswitches the power supply unit to the operation mode, in response todetection by the states monitor unit of a change from the connectionstate to the non-connection state, when the power supply unit is in thepower saving mode.
 8. An image forming apparatus according to claim 7,wherein the power supply unit includes a communication function switchunit which switches, in the power saving mode, the communicationinterface between a communication enabling mode and a communicationdisabling mode, the communication enabling mode in which operatingelectric power necessary for data communication performed by thecommunication interface is supplied to the communication interface, thecommunication disabling mode in which stand-by electric power having alevel at which communication is disabled is supplied to thecommunication interface, and the mode switch unit causes thecommunication interface to be kept in the communication enabling modeaccording to the connection state of the communication interfacedetected by the states monitor unit, and the mode switch unit causes thecommunication interface to be switched to the communication disablingmode according to the non-connection state of the communicationinterface detected by the states monitor unit, when the operation modeis switched to the power saving mode.
 9. An image forming apparatusaccording to claim 7, comprising a communication interface having apower line, wherein the states monitor unit detects the connection stateand the non-connection state of the communication interface based on apotential of the power line of the communication interface.
 10. An imageforming apparatus according to claim 8, comprising a communicationinterface having a power line, wherein the states monitor unit detectsthe connection state and the non-connection state of the communicationinterface based on a potential of the power line of the communicationinterface.
 11. An image forming apparatus according to claim 7,comprising a communication interface which mediates the datacommunication while a data link is established, wherein the statesmonitor unit detects the connection state and the non-connection stateof the communication interface based on presence or absence of the datalink establishment of the communication interface.
 12. An image formingapparatus according to claim 8, comprising a communication interfacewhich mediates the data communication while a data link is established,wherein the states monitor unit detects the connection state and thenon-connection state of the communication interface based-on presence orabsence of the data link establishment of the communication interface.